1. Field of the Invention
Exemplary aspects of the present invention generally relate to a fixing device and an image forming apparatus such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof including the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member; an optical writer projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
The fixing device used in such image forming apparatuses may include a pair of looped belts or rollers, one being heated by a heater for melting toner (hereinafter referred to as “fixing member”) and the other being pressed against the fixing member (hereinafter referred to as “pressing member”). In a fixing process, the fixing member and the pressing member meet and press against each other, forming a so-called fixing nip through which a recording medium passes to fix a toner image thereon under heat and pressure.
Toner used in such fixing devices generally contains resin material. When melted in the fixing nip, the toner in the toner image on the recording medium tends to stick to the fixing member, winding around the fixing member even after the recording medium exits the fixing nip, causing a paper jam. To address such difficulty, a wax component is added to the toner, or alternatively, the fixing member is covered with a release agent such as silicone oil, to prevent the toner in the toner image sticking to the fixing member.
To facilitate separation of the recording medium bearing the melted toner from the fixing member, a separation mechanism including a separation claw is provided to separate physically the recording medium undesirably wound around the fixing member from the fixing member.
However, there is a drawback to this configuration in that the separation claw of the separation mechanism contacts slidably the fixing member, and thus toner accumulates easily at a portion where the separation claw and the fixing member meet. When the accumulated toner reaches a certain amount, the toner separates from the contact portion, thereby contaminating the recording medium. Furthermore, such a separation claw slidably contacts the fixing member while rotating, leaving a trace of slide on the surface of the fixing member, thereby yielding a resulting image with streaks.
In recent years, however, because of difficulty in handling of the release agent such as the silicone oil, application of such a release agent on the surface of the member becomes less frequent, complicating efforts to separate reliably the recording medium bearing the toner image from the fixing member.
To counteract such difficulty, a contactless separation plate disposed very close to the fixing member is proposed.
In order to obtain similar reliable separation ability as the separation claw that directly contacts the fixing member, the space between the contactless separation plate and the fixing member needs to be minute and adjusted by 0.1 mm, for example. Furthermore, the separation plate needs to be disposed as close to the nip exit as possible.
For example, a known approach includes a separation guide provided with a curved member (contact members) at both ends of the separation guide in an axial direction. The separation guide is disposed at the nip exit. A certain amount of the space between the separation guide and the fixing member is maintained by the curved members that contact both ends of the fixing member in the axial direction thereof outside a maximum image area where the recording medium of a maximum size will not pass.
Although advantageous and generally effective for its intended purpose, there is a drawback to this configuration that the separation guide is made of molded heat resistant resin and deforms due to twist against the axial direction, complicating efforts to maintain the gap of 0.1 to 0.6 mm between the separation guide and the fixing member along the axial direction.
Such deformation of the separation guide in the direction of twist relative to the axial direction causes a difference in a contact pressure of the curved member (contact members) at each end contacting the rotating fixing member. Consequently, the curved member having the higher contact pressure against the fixing member damages the fixing member.